The invention relates in general to the field of micro- or nanofluidic devices with channels having ratchet topographies, and in particular to devices that enable rocking ratchets.
Microfluidics generally refers to microfabricated devices, which are used for pumping, sampling, mixing, analyzing and dosing liquids. Prominent features thereof originate from the peculiar behavior that liquids exhibit at the micrometer length scale. Volumes well below one nanoliter can be reached by fabricating structures with lateral dimensions in the micrometer range. Many microfluidic devices have user chip interfaces and closed flowpaths. Closed flowpaths facilitate the integration of functional elements (e.g., heaters, mixers, pumps, UV detector, valves, etc.) into one device while minimizing problems related to leaks and evaporation. Nanofluidic devices are similar devices, though at least some of the characteristics dimensions of liquid-containing features reach the nanometer range.
Devices that can shuttle, separate, mix and collect nanoscale particles (such as a metallic nanoparticle, quantum dots or biomolecules) have immediate applications in nanofluidics, ranging from material science to lab on chip devices for point of care diagnostics and bio-chemistry.
Inspired by molecular motors in biology, artificial Brownian motors were proposed for selective particle transport using an asymmetric energy landscape and non-equilibrium fluctuations. Previous experimental investigations of such Brownian motors focused on mechanisms that exploit isotropic diffusion and a periodically generated, asymmetric trapping potential to transport micron scale particles. The required potentials were obtained using optical or dielectrophoretic forces, which scale with particle volume and are therefor not efficient at the nanoscale. In particular, the transport of DNA molecules was demonstrated using direct charge-charge interactions with intercalated electrodes.
While flashing ratchets rely on diffusion, designs of rocking ratchets have been proposed that may generate directed particle motion based on a fluctuating external force and a static potential landscape. However, to date, rocking Brownian motors have not been experimentally demonstrated for nanoscale particles, owing to the difficulty of creating a sufficiently strong and reliable static energy landscape.